The invention pertains to a device for transferring device heat between a heat source and a heat sink by means of thermal conduction. Such a heat exchanger is used, in particular, in industrial electronics in order to dissipate the thermal power loss of electronic components.
Electronic components such as, for example, microprocessors are positioned on printed circuit boards that are typically installed in a housing. In a so-called single board computer, all essential electronic components of the computer are arranged on a single printed circuit board, namely the so-called motherboard. The formats of these motherboards have the tendency to become smaller and smaller such as, for example, the standardized Mini-ITX with dimensions of 170×170 mm, in the center of which a powerful processor is positioned.
Modern multi-core processors with high clock rate have such a high thermal power loss that they require purposeful cooling in order to operate reliably. This is typically realized with the aid of a heat sink that is attached to the planar surface of the processor and features a plurality of cooling ribs such that the waste heat can be dissipated into the surrounding air from a large surface by means of convection.
In many applications, the electronic components of a device need to be enclosed in a housing in order to protect them from dust, moisture and perturbing radiation. The housing may feature air inlet and air outlet openings and/or be equipped with an electric fan that blows cooling air through the housing in order still dissipate the waste heat generated in the interior of the device outward. However, a completely closed housing is required in many applications in order to fulfill stricter requirements with respect to the protection against dust and moisture.
Housings for electronic devices, particularly industrial computers with higher IP protection rating, are tightly closed all around such that cooling air can no longer be conveyed through the housing. Instead, such closed housings feature on their outer sides large heat sinks that are realized, for example, in the form of extruded profiles. In this case, it is problematic to thermally connect the electronic components in the interior of the housing, particularly the processor or the processors, to the heat sinks on the outer side of the housing such that the thermal power losses can be transferred to the heat sinks by means of thermal conduction and then dissipated into the surroundings by means of convection and/or thermal radiation.
It is known to use massive metal blocks that are attached to the processor with their underside and contact the inner side of a housing wall with their upper side in order to transfer heat from the processor to the housing wall. In this case, one problem can be seen in the relatively broad tolerances of the electronic and mechanical components, particularly the processors and the components of the protective housing. Just the structural height of a commercially available processor in the installed state has a typical tolerance of up to 1 mm. This is the reason an elastic or pasty material with sound thermal conductivity is frequently used at the heat transfer point. However, the thickness of the layer of thermally conductive paste needs to be maintained as small as possible because even the thermal conductivity of the best products available is several orders of magnitude lower than the thermal conductivity of metal, for example aluminum. The thermal resistance becomes even higher if the other end of the metal block is also brought in thermal contact with the housing wall by means of thermally conductive pastes.
In the construction and production of standardized small housings for industrial computers, another problem can be seen in that it should be possible to use different types of processors although the dimensions of the printed circuit board are predefined. Processors with different performance of different manufacturers such as Intel, AMD, ARM or VIA not only differ with respect to their electronic parameters and thermal power losses, but also with respect to their geometric dimensions. Although heat sinks and heat exchangers that can be universally utilized are offered for these processors, the required installation material must compensate the tolerances for the entire construction. The tolerances for the thickness of the processor, the socket, the heat sink or heat exchanger and, if applicable, the housing therefore add up to a value on the order of 2 mm or even more. Such large tolerances can no longer be compensated with thermally conductive paste or so-called gap filler if effective cooling should still be ensured.
Another challenge in this context can be seen in that at least the upper cover of a completely closed housing should be removable in order to access the enclosed electronics when necessary. When the cover is replaced after a repair, the thermal conductivity between the processor and the cover also needs to be completely restored. However, thermally conductive paste is not well suited for multiple use.
US 2007/0030656 A1 describes a thermal transferring device with variable height. It comprises two massive bodies that engage into one another, wherein the first body is in contact with a heat-emitting component and the second body can be vertically displaced relative to the first body. A spring is arranged between the two bodies and presses the upper body upward against the inner side of a housing cover. The spring pressure ensures that the upper body is always in contact with the housing cover, namely even if its height relative to the bottom of the housing varies, for example, due to manufacturing tolerances. In this known heat exchanger, the lower thermally conductive body is realized in the form of a piston and the upper thermally conductive body is realized in the form of a cylinder, in which the piston can slide up and down. This results in long vertical gaps between the two bodies that interrupt the heat transfer over a large surface. The gap or the clearance between the two bodies cannot fall short of a certain minimum dimension if the mobility of the two bodies relative to one another should not be impaired or even inhibited. It is therefore proposed to apply a lubricant, preferably a lubricating oil with increased thermal conductivity, onto the surfaces that slide relative to one another.